The good news was that we had a decision at all. Had things not gone well with the last MRD test our options would have been looking grim. This was a test to find out the extent to which Henry’s leukaemia was in retreat by looking at the “minimal residual disease”.

The news came while I was sitting in a conference listening to a pollster explaining what the public thought of the NHS. I imagine what he said was largely positive but I can’t tell you as I spent the talk speaking first to Great Ormond Street and then to Celia and then unchoking myself.

Henry is not considered to be at high risk from his disease. He is intermediate risk. These hardly appear to be consoling words. But they spelled the difference between a defined three years of chemotherapy (the path we are now on) or a much more aggressive treatment with the likelihood of a bone marrow transplant with the months of quarantining, uncertainty and heartache that would have brought with it. This is not a choice you would ever want but that’s one of the reasons why this serious disease is serious.

So here we are – three years to go. We know the treatment end date in May 2016. Henry will be nine. But first we face an enormous dilemma: Henry was placed randomly by a computer into one of the arms of the clinical trial he is taking part in. There are four arms… three compare existing treatments, the fourth tries an untested regimen.

First, the American model: Patients are given high doses of a chemotherapy called methotrexate, where they spend several days each fortnight in hospital. They are monitored and then “rescued” from the poisonous effects of the drugs. Then later they are given “pulses” of the steroid dexamethasone and vincristine for a couple of weeks. Both have nasty side-effects. “Dex” as it is known causes big mood swings, hunger pangs and leg pain; vincristine also hobbles the children and causes their hair to drop out.

Second, the German model: This is similar to the American treatment plan but without the pulses of dexamethasone or vincristine.

The third is the British model: Known as Capizzi, this sees the chemotherapy increased gradually until the patient can just tolerate it. The advantage is there is no need for a rescue and therefore no scheduled hospital stays. But it is followed as with the Americans by pulses of Dexamethasone and vincristine.

The fourth is untried: It combines the British and German models. Patients are treated on the Capizzi regimen but they don’t have the pulses.

Guess which one Henry’s on?

Of course he is.

The one arm that we knew would cause us the most soul-searching and uncertainty: the fourth on the list – the untried model. We have decided to keep Henry in the trial. But we genuinely don’t know and cannot know if we have made the right decision. We can change our minds at any time and revert to the usual protocol: Capizzi with pulses.

Henry is currently being given methotrexate into his spine and through a drip. He’s getting the old leukaemia starver asparaginase (injected into his leg) and vincristine (intravenous) the drug that tightens his leg muscles and makes his hair fall out. But he will not have the later pulses of vincristine nor the dex.

So why the quandary? Not only is Henry in the untried model, it is the one where he appears to get least treatment. Sure he will also get the least toxic treatment, but will it be enough to see off the leukaemia for good? The problem is that with the German model treatment is aggressive from the start, whereas Capizzi increases over time. So with the German model, at least you’ve given the leukaemia a good blasting right from the start even if you then take away the pulses. With the untried model, the attack on the leukaemia ramps up. Is the tried and tested Capizzi model successful because the later pulses see off the disease? What happens if you take away the pulses? By keeping Henry in this trial, are we exposing him to unnecessary risk?

Henry has been coping really well with his chemotherapy. This weekend he charged about with his cousins and relived the Olympics.

I’m acutely aware that we are not in possession of all the facts – not least because we do not have the years of training to fully understand them. Without that we have to have trust and faith.

We have grilled the consultants and nurse consultants and researchers… and we will do so again. There should be no inference that our consent is not informed. It is. But in the end this is a decision about trust and faith. Do we trust the medics, researchers and ethics committee and trial framers and scientists enough?

These are the people who have successfully increased cure rates from childhood leukaemia to above 90%. These are the people who are behind possibly the biggest success story in cancer research and treatment. Without the families of children, like Henry, being prepared to trust them, without children taking part in clinical trials, leukaemia treatment would not be so successful.

This is quite easily the single toughest decision we have ever, ever had to make. And I hope we never face anything so challenging again. You may well think we have made the wrong call… but trust in our researchers and trust in the scepticism of the people who reviewed this trial and the systems of review are important.

I hope we have made a reasoned and reasonable decision. The costs of the wrong call are unbearably high. But so is the cost of people not taking part. Again it comes back to the old refrain – we are a community. We have learned to have faith in it.